1. Field of the Invention
The present invention relates generally to the art of multilayered coatings providing high transmittance and low emissivity, to articles including substrates having such coatings deposited thereon, and more particularly to coatings formed of metal and metal oxides deposited on transparent substrates.
2. Discussion of the Presently Available Technology
High transmittance, low emissivity multilayer coatings on transparent substrates, such as glass, provide coated articles which transmit visible light while minimizing the transmittance of other wavelengths of light, such as light in the infrared spectrum. Such articles are particularly useful as automotive or architectural glass because they allow the transmission of visible light therethrough, but minimize radiative heat transfer associated with infrared light.
High transmittance, low emissivity coatings generally include a reflective metal layer which provides the infrared reflectance and low emissivity, between dielectric, antireflective layers of metal oxides to reduce the visible reflectance. These multilayer coatings are typically produced by cathode sputtering, especially magnetron sputtered vacuum deposition.
U.S. Pat. No. 4,610,771 to Gillery provides multilayer coatings including a silver reflective metal layer and zinc-tin alloy oxide layers for use as a high transmittance, low emissivity coating.
U.S. Pat. No. 4,806,220 to Finley discloses a multilayer coating suitable for high temperature processing. A type of this coating utilizes metal primer layers e.g. a pair of titanium primer layers, one above and one below a reflective metal layer.
High transmittance, low emissivity coatings over transparent substrates such as glass, are susceptible to mechanical damage, including but not limited to the formation of surface scratches. The coatings may be scratched when the coated substrates are shipped or subjected to manufacturing processes. For example, when the substrate is a coated glass sheet, these manufacturing processes may include cutting operations, seaming operations, and washing operations. Washing operations may include the use of abrasive brushes or cleaners. The seaming process is essentially a sanding operation which removes edge defects that can cause breakage during tempering, and residual abrasive particles, e.g. dust, may remain on the glass surface after seaming which may tend to scratch during, for example, during subsequent washing operations. Even operations which by themselves may not tend to scratch the surface of the coating, as for example heating processes such as bending, tempering, annealing, and the like, may cause surface scratching as the substrate is handled, e.g. loaded and/or unloaded into and out of the equipment, e.g. a furnace, necessary to perform the heating process. Further, where a coating has surface scratches and is then subjected to a high temperature processing operations, (e.g. tempering), scratches present on or about the coating surface may become even more visible to the unaided eye as a result of the high temperature processing operation.
As can be appreciated by those skilled in the art of producing coating surfaces or handling coated surfaces, it would be desirable to improve the scratch resistance of coatings, particularly high transmittance low emissivity coatings deposited over substrates, such as transparent glass substrates, particularly those expected to be subjected to high temperature processing.